On Fri, 14 Sep 2007 10:51:07 -0700, "Matt Barrow"
wrote:


wrote in message
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On Thu, 13 Sep 2007 19:45:44 -0700, "Matt Barrow"
wrote:
An irrelevant question if you can't get there in the first place. But
if
you want an answer just look at the standard lapse rate as a start.

Remember, too, that a thermometer held in the sun is going to read higher
than a thermometer in the shade. What it's reading is the sunlight on skin
or a thermometer, not the air temp. That's why they takes temps in the
shade -- the heat transfer is much different.


That is the reason for my question.

Surely standard lapse rate does not apply?

SLR is only a _standard_ rate. It can be effected by pressure, inversions,
wind, even the terrain. In this latter point, it's probably nullified in
the first hundred or so feet.


I'm wondering if the ground temperature will reduce quickly as you
climb.
That would depend on several factors including those mentioned above. A wind
shear would probably have a great effect.

In other words will the air temperature drop quickly as you
leave ground effect or will it continue for many tens of feet?

Ground effect can be ten feet, or a few hundred. It would be different if
the runway surface was asphalt as opposed to concrete (different albedo).

I presume if there's any cross wind the hotter air above the runway
will drift sideways so maybe the effect will be less..

Possibly, but it would depend on the wind SPEED.

I am not pre-judging the cause of the accident but there has been
mention of high temperature above the runway causing a higher density
altitued than perhaps calculated. Since I usaully fly in a low level
and colder climate (UK) where density altitude is mostly of little
importance I was interested in the effects. My only experience is from
a long runways in Palm Springs (100°F) and Minden (near Tahoe) with
runway around 5000ft and maybe 80°F.

From comments it would appear that at take-off density altitude may be
higher than expected but soon after take-off your density altitude
would reduce quite quickly.

Re. Ground Effect, I thought that was normally within about one
wingspan?

Thanks for the input.